Academic journal article Genetics

Cis-Effects on Meiotic Recombination across Distinct A1-Sh2 Intervals in a Common Zea Genetic Background

Academic journal article Genetics

Cis-Effects on Meiotic Recombination across Distinct A1-Sh2 Intervals in a Common Zea Genetic Background

Article excerpt

ABSTRACT

Genetic distances across the a1-sh2 interval varied threefold in three near-isogenic stocks that carry structurally distinct teosinte A1 Sh2 haplotypes (from Z. mays spp. mexicana Chalco, Z. mays spp. parviglumis, and Z. luxurians) and a common maize a1::rdt sh2 haplotype. In each haplotype >85% of recombination events resolved in the proximal 10% of the ~130-kb a1-sh2 interval. Even so, significant differences in the distributions of recombination breakpoints were observed across subintervals among haplotypes. Each of the three previously detected recombination hot spots was detected in at least one of the three teosinte haplotypes and two of these hot spots were not detected in at least one teosinte haplotype. Moreover, novel hot spots were detected in two teosinte haplotypes. Due to the near-isogenic nature of the three stocks, the observed variation in the distribution of recombination events is the consequence of cis-modifications. Although generally negatively correlated with rates of recombination per megabase, levels of sequence polymorphisms do not fully account for the nonrandom distribution of recombination breakpoints. This study also suggests that estimates of linkage disequilibrium must be interpreted with caution when considering whether a gene has been under selection.

HOMOLOGOUS recombination provides physical connections between pairs of homologous chromosomes during meiosis and thereby helps to prevent nondisjunction. In addition, meiotic recombination generates novel haplotypes upon which natural selection can act. Two types of recombination events result from meiotic recombination: reciprocal crossovers (CO) and unidirectional noncrossovers (NCO). Although evidence from yeast has shown that both events are initiated by doublestrand breaks (DSB) (reviewed by PAQUES and HABER 1999), these two types of events probably arise via different pathways (ALLERS and LIGHTEN 2001; HUNTER and KLECKNER 2001; CLYNE et al 2003). COs are thought to arise via the DSB repair pathway (SzOSTAK et al. 1983; CAO et al. 1990; SUN et al. 1991), which involves the formation of double Holliday junctions (DHJs) following strand invasion; resolution of these DHJs can result in COs. Although NCOs could also arise via this pathway (following an alternative resolution of DHJs), several pieces of evidence suggest that NCO events may instead arise from the synthesis-dependent strand-annealing pathway that does not involve the formation of DHJs (reviewed by PAQUES and HABER 1999; ALLERS and LIGHTEN 2001; HUNTER and KLECKNER 2001).

Meiotic recombination does not occur randomly in a genome or across a chromosome. Eukaryotic genomes contain recombination hot and cold spots where the rates of recombination per megabase are much higher and lower, respectively, than average (reviewed by LIGHTEN and GOLDMAN 1995; PUCHTA and HOHN 1996; SCHNABLE et al. 1998; PETES 2001). Surprisingly, although the DNA sequences of the human and chimp genomes are highly similar, some human hot spots (e.g., TAP2) are not conserved in chimps (PENNISI 2004; PTAK et al 2004). This is consistent with the finding that within a species, as- and Éraws-genetic modifiers can affect the nonrandom occurrence of meiotic recombination in a genome. Cz's-regulation of recombination has been demonstrated in studies of fungi, mammals, and plants. In fungi, hot spots are classified as á, â, and γ according to the natures of the sequences that cause the hyperrecombination activity (reviewed by PETES 2001). á-hot spots are caused by sequences that are transcription factor binding sites and that require the binding of transcription factors to activate the hot spot, â-hot spots are caused by sequences that are thought to cause the exclusion of nucleosomes, resulting in higher accessibility of a region to the recombination machinery. ~/-hot spots are associated with sequences with high G + C content. In addition to the natures of sequences within or in the vicinity of a hot spot that can regulate recombination in as, sequence polymorphisms between DNA segments residing on a pair of homologs can affect both recombination rates per megabase and the distribution of recombination events. …

Search by... Author
Show... All Results Primary Sources Peer-reviewed

Oops!

An unknown error has occurred. Please click the button below to reload the page. If the problem persists, please try again in a little while.